1. Field of the Invention
The present invention relates to a method for producing a bioalcohol. More specifically, the present invention relates to a method for increasing the productivity of a bioalcohol in which hydrophobically modified hydrophilic nanoparticles, such as silica nanoparticles, are used to enhance the solubility of syngas in a fermentation process.
2. Description of the Related Art
Bioenergy has been most widely developed and utilized in recent years due to its potential to replace fossil fuels. Particularly, lignocellulosic biomass-based ethanol production technology has an advantage in that raw materials therefor are abundant anddiverse.
Major methods for producing bioethanol from lignocellulosic biomass include a saccharification-fermentation processand a gasification-fermentation process. According to the saccharification-fermentation process, pretreated lignocellulosic biomass is saccharified by hydrolysis and fermented to produce ethanol. According to the gasification-fermentation process, lignocellulosic biomass is gasified to produce syngas composed of carbon monoxide, carbon dioxide, and hydrogen, followed by fermentation of the syngas to produce ethanol. The saccharification-fermentation process involves complex pretreatment and hydrolysis steps to produce monosaccharides, which are used in subsequent fermentation. Accordingly, the saccharification-fermentation process is disadvantageous in terms of time and cost. In contrast, the gasification-fermentation process does not require saccharification and is thus advantageous in that ethanol can be obtained in a relatively simple manner. Another advantage of the gasification-fermentation process is that the gasification is independently used for heat/power production because syngas can be used as an electricity or heat energy source through combustion. Raw materials for syngas production can be extended to organic waste, such as agricultural waste, as well as lignocellulosic biomass.
Particularly, research on the production of valuable substances from syngas is extremely limited. A catalytic reaction may be used as achemical method for the production of a valuable substance from syngas. In this case, since the reaction is highly sensitive to the presence of small amounts of impurities, syngas containing large amounts of impurities should undergo purification to produce a valuable substance, such as a synthetic oil. Alternatively, a biological method may be applied to the production of a valuable substance from syngas. The biological method does not require highly pure reactants, unlike catalytic reaction. Therefore, the syngas can be directly used without further purification. The reaction is carried out under ambient temperature and pressure conditions, which is advantageous in terms of initial investment and operating costs.
Carbon monoxide, carbon dioxide, and hydrogen are converted into various substances by aerobic or anaerobic microorganisms. Some anaerobic microorganisms were reported to have the ability to produce ethanol from carbon monoxide, carbon dioxide and hydrogen substrates. Particularly representative examples of such microorganisms include Clostridium ljungdahlii, Eubacterium limosum, and Peptostreptococcus productus. 
However, it is very difficultfor microorganisms to utilize carbon monoxide, carbon dioxide, and hydrogen as main substrates for biological conversion due to extremely low solubilities thereof. For this reason, the conversion of the gases into organic acids or bioalcohols such as ethanol remains at a negligible level, which limits its application to mass production.